EP2000567B1

EP2000567B1 - Method for growing iii nitride single crystal

Info

Publication number: EP2000567B1
Application number: EP07739311.4A
Authority: EP
Inventors: Michimasa Miyanaga; Naho Mizuhara; Shinsuke Fujiwara; Hideaki Nakahata; Tomohiro Kawase
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 2006-03-29
Filing date: 2007-03-22
Publication date: 2014-12-31
Anticipated expiration: 2027-03-22
Also published as: EP2000567A4; EP2000567A2; WO2007111219A1; EP2000567A9; US8361226B2; KR20080103955A; US20100147211A1; JPWO2007111219A1; CN101351579B; CN101351579A; KR101346501B1; JP5374872B2

Description

Technical Field

The present invention relates to methods of growing Group III nitride single crystals utilized in substrates for light-emitting diodes, electronic devices, semiconductor sensors, and other semiconductor devices. In particular the invention relates to a method of growing low-dislocation-density III-nitride single crystals of favorable crystallinity.

Background Art

III-nitride crystals such as Al _x Ga_1-xN (0 < x ≤ 1, likewise hereinafter) single crystals are extraordinarily useful as materials for building semiconductor devices such as light-emitting diodes, electronic devices, and semiconductor sensors.
Examples that have been proposed of how to manufacture such III-nitride single crystals include vapor-phase techniques, particularly among which sublimation has been singled out from the perspective of obtaining crystals of satisfactory crystallinity with a narrow full-width at half-maximum for the X-ray diffraction peak. (Cf., for example, the specifications for U.S. Pat. No. 5,858,086 (Patent Document 1), U.S. Pat. No. 6,296,956 (Patent Document 2), and U.S. Pat. No. 6,001,748 (Patent Document 3).)
However, with attempts to manufacture by sublimation a bulk III-nitride single crystal-for example (repeated similarly hereinafter), 2 inches (approximately 5.08 cm) in diameter × 2 mm or more in thickness-leading, due principally to the fact that no high-quality crystals ideal for undersubstrates exist, to problems of crystal growth being nonuniform and of increased dislocation density, crystallinity degradation, and incidents of polycrystalization, methods of stably growing Al _x Ga_1-xN single crystal of practicable size, and of low dislocation density and favorable crystallinity have vet to be proposed.
JP 2006 027988 A relates to a method for producing a nitride single crystal in which a source material for a nitride single crystal is heated and sublimated in a heating furnace, and a sublimated source material is crystallized on a seed crystal disposed in the furnace to grow a single crystal.
WO 00/22204 A relates to synthetic gemstones formed from colorless aluminum nitride single crystals, and colorless aluminum nitride silicon carbide alloy single crystals. Bulk AlN:SiC single crystals are grown using pure polycrystalline AlN:SiC source crystals having a ratio of approximately 70 atomic % AlN and 30 atomic % SiC. The bulk single crystal of AlN:Sic may be grown by vaporizing individual aluminum and silicon liquid baths, i.e., contained in the two different source compartments, to produce Al and Si source vapor in the growth crucible with C and N vapor species.
WO 2006/110512 A , being only relevant for the question of novelty, discloses a method of growing bulk single crystals of AlN on a single crystal seed, wherein the AlN source material is placed within a crucible chamber in spatial relationship to seed fused to the cap of the crucible. The source material is sublimed and deposited on the seed, thereby growing a bulk single crystal of AlN.

Patent Document 1: U.S. Pat. No. 5,858,086 specification
Patent Document 2: U.S. Pat. No. 6,296,956 specification
Patent Document 3: U.S. Pat. No. 6, 001, 748 specification

Disclosure of Invention

Problem Invention is to Solve

An object of the present invention is to make available a method of stably growing bulk III-nitride single crystal of low dislocation density and favorable crystallinity.

Means for Resol ving the Problem

The present invention relates to a III-nitride single-crystal growth method according to claim 1.

Effects of the Invention

The present invention affords a method of stably growing bulk III·nitride single crystals of low dislocation density and of favorable crystallinity.

Brief Description of Drawings

Fig. 1 is a cross-sectional schematic diagram for illustrating a III-nitride single-crystal growth method involving the present invention.
Fig. 2 is a cross-sectional schematic diagram for illustrating the III-nitride single-crystal growth method involving the present invention.
Fig. 3 is a cross-sectional schematic diagram for illustrating the III-nitride single-crystal growth method involving the present invention.
Fig. 4 is a cross-sectional schematic diagram for illustrating the III-nitride single-crystal growth method involving the present invention.
Fig. 5 is a cross-sectional schematic diagram for illustrating the embodiment of a III-nitride single-crystal growth method involving the present invention.
Fig. 6 is a cross-sectional schematic diagram for illustrating the embodiment of the III-nitride single crystal growth method involving the present invention.

Legend

1: source material: 2: Al _y Ga_1-yN source; 3: impurity element; 4: Al _x Ga_1-xN single crystal; 5: Al _s Ga_1-sN single crystal: 7: Al _t Ga_1-tN source; 9: undersubstrate; 10: sublimation furnace; 11: reaction chamber; 11a: N₂ gas inlet; 11c N₂ gas outlet; 12: crucible; 12a, 12b, 12c, and 12e: ventilation openings; 12p: first source material compartment; 12q: second source material compartment; 12r: crystal-growth compartment; 13: heater; 14: high-frequency heating coils; 15: radiation thermometers; 16: undersubstrate protector.

Best Mode for Carrying Out the Invention

Disclosure Mode

1

The III-nitride single crystal growth method involving the present invention is characterized in being furnished with a step of , referring to Fig. 1, placing source material 1 in a crucible 12, and a step of sublimating the source material 1 to grow an Al _x Ga_1-xN (0 < x ≤ 1, hereinafter) single crystal 4 in the crucible 12, and characterized in that the source material 1 is composed of Al _y Ga_1-yN (0 < y ≤ 1, hereinafter) source 2 and impurity element 3, and the impurity element is at least a single kind element selected from the group consisting of IVb elements and IIa elements.
By including, for the sublimation source material 1, the Al _y Ga_1-yN source 2 that is a direct source material for forming the Al _x Ga_1-xN single crystal 4, together with at least a single kind of impurity element 3 selected from the group consisting of IVb elements and IIa elements, the rate at which the Al _x Ga_1-xN single crystal 4 grows heightens, to grow bulk Al _x Ga_1-xN single crystal 4 of low dislocation density and favorable crystallinity stably. Such an impurity element E is believed to react with A1 to become Al _p E _q (g) (herein, p and q are positive numbers), and to act as material for transporting Al during growth of the Al _x Ga_1-xN single crystal 4, heightening the crystal growth rate, as well as reducing dislocation densities to enhance crystallinity.
Herein, it is sufficient that the source material 1 includes the Al _y Ga_1-yN source material 2 and at least a single kind of impurity element 3 selected from the group consisting of IVb elements and IIa elements, and the manner in which they are included in the source material is not limited. Therefore, the Al _y Ga_1-yN source 2 collectively and the impurity element 3 collectively may be each arranged in the crucible 12, as illustrated in Fig. 1. Also as illustrated in Fig.2, the Al _y Ga_1-yN source 2 and impurity element 3 may be arranged mixed together in the crucible 12. Furthermore, as illustrated in Fig. 3, with a first and a second source material compartments 12p, 12q where gases in the compartments can be exchanged via a ventilation opening 12a being provided in the crucible 12, the Al _y Ga_1-yN source material 2 may be arranged in the first source material compartment 12p, and the impurity element 3 in the second source material compartment 12q.
Moreover, what form the Al _y Ga_1-yN source material 2 and impurity element 3 have is not particularly limited as long as the Al _y Ga_1-yN source material 2 and impurity element 3 are in the form that enables controlling their relative proportions-that is, if in solid form, they may be block-like, granular, and powdery. It should be understood that in the situation in which the crucible 12, and the source material compartments 12p, 12q and crystal-growth compartment 12r that will be explained hereinafter are formed of the impurity element 3, the concentration of the impurity element 3 cannot be controlled, which prevents above impurity element effect from being brought during Al _x Ga_1-xN single crystal growth. Additionally, the chemical composition of the Al _y Ga_1-yN source material 2 and that of the Al_xGa_1-xN single crystal 4 produced from it coincides with each other when x = y = 1, but generally differ from each other except when x = y = 1 in accordance with the conditions on which the Al _y Ga_1-yN source is sublimated, and with the conditions on which the Al _x Ga_1-xN single crystal 4 is grown. Once the sublimation conditions on the Al _y Ga_1-yN source and the growth conditions on the Al _x Ga_1-xN single crystal 4 are defined, what chemical composition of the Al _y Ga_1-yN source material 2 is required to produce the Al _x Ga_1-xN single crystal having the given chemical composition is determined.
Herein, the sublimation method utilized means the method in which, referring to Fig. 1, the source material 1 including the Al _y Ga_1-yN source 2 is sublimated, and then is solidified again to produce the Al _x Ga_1-xN single crystal 4. During sublimation crystal growth, a vertical high-frequency-heating sublimation furnace 10 as illustrated in Fig. 1 is employed, for example. The WC crucible 12 having a ventilation opening 12e is disposed in the center part of a reaction chamber 11 in the vertical sublimation furnace 10, with a heater 13 being provided around the crucible 12 so that ventilation from the inside of, to the outside of, the crucible 12 is secured. Furthermore, high-frequency heating coils 14 for heating the heater 13 are disposed centrally along the outer side of the reaction chamber 11. Additionally, an N₂ gas inlet 11a for passing N₂ gas into the reaction chamber 11 outside of the crucible 12, an outlet 11c, and radiation thermometers 15 for measuring the temperatures of the bottom and top sides of the crucible 12 are provided to the ends of the reaction chamber 11.
Referring to Fig. 1, in the following manner, the Al _x Ga_1-xN single crystal 4 can be manufactured employing above vertical sublimation furnace 10. The source material 1 including the Al _y Ga_1-yN source 2 and impurity element 3 are housed in the lower part of the crucible 12, and with the N₂ gas being continuously passed into the reaction chamber 11, the temperature in the crucible 12 is raised by heating the heater 13 employing the high-frequency heating coils 14, and the temperature of the part in the crucible 12 where the source material 1 is housed is kept higher than that of the rest in the crucible 12, to sublimate the Al _x Ga_1-xN and impurity element in the source material 1, and then the Al _x Ga_1-xN is solidified again in the upper part of the crucible 12 to grow the Al _x Ga_1-xN single crystal 4.
Herein, as a result of, during the growth of the Al _x Ga_1-xN single crystal 4, bringing the temperature of the part in the crucible 12 where the source material 1 is housed to a level of 1600°C to 2300°C, and making the temperature of the upper part in the crucible 12 (where the Al _x Ga_1-xN single crystal 4 is grown) approximately 10°C to 200°C lower than that of the part in the crucible 12 where the source material 1 is housed, the Al _x Ga_1-xN single crystal 4 of favorable crystallinity can be obtained. Moreover, passing N₂ gas into the reaction chamber 11 outside the crucible 12 continuously also during crystal growth reduces the mixing of the impurities into the Al_xGa_1-xN single crystal 4.
In addition, during temperature rising in the crucible 12, making the temperature of the part in the crucible 12 except where the source material is housed higher than that of the part in the crucible 12 where the source material 1 is housed removes impurities via the ventilation opening 12e from the crucible 12, making it possible to further reduce the mixing of the impurities into the Al _x Ga_1-xN single crystal 4.
The impurity element is at least a single kind element selected from the group consisting of IVb elements and IIa elements. The IVb and IIa elements, which are believed to act as materials for transporting Al, heightens Al _x Ga_1-xN single crystal growth rate and enhances crystallinity. Herein, Group IVb elements mean elements categorized into Group IVb in periodic table of the elements, and C (carbon), Si (silicon), and Ge (germanium) fall into the Group IVb. On the other hand, Group IIa elements , which are called also alkaline earth metal, mean elements categorized into Group IIa in periodic table of the elements, and Mg (magnesium) and Ca (calcium) fall into the Group IIa. A plurality of impurity elements selected from above IVb and IIa elements can be used at the same time. Selecting a plurality of elements (for example, Si and C) from IVb elements is less than optimal, however, because the selected plurality of elements (Si and C) react with each other to form a stable compound (SiC), and thus lose the effect of acting as materials for transporting Al, sometimes resulting in failure to offer advantages sufficient to heighten Al _x Ga_1-xN single crystal growth and to enhance crystallinity
Herein, the impurity element is preferably any one of Si, C, and Ge. As to the above impurity element, any one specific element picked out from IVb elements-particularly, Si, C, or Ge among them-is preferable from the perspective of heightening Al _x Ga_1-xN single crystal growth rate and of enhancing crystallinity.
In source material 1 of this embodiment, ratio n_E /n_A (simply, molar ratio n_E /n_A , hereinafter) of the number of moles n_E of the atoms of the impurity element 3 to the number of moles n_A of the Al atoms in the Al _y Ga_1-yN source 2 is between 0.01 and 0.5 inclusive, and more preferably, is between 0.05 and 0.5 inclusive. At a molar ratio n_E /n_A of less than 0.01, the impurity element has an attenuated effect of acting as material for transporting Al, and at a molar ratio n_E /n_A of more than 0.5, growth of the Al _x Ga_1-xN single crystal 4 is blocked.
Furthermore, ratio n_E /n_o (simply, molar ratio n_E /n_o , hereinafter) of the number of moles n_E of the atoms of the impurity element 3 to the number of moles n_o of the atoms of oxygen contained in the source material 1 is between 2 and 1 × 10⁴ inclusive. Because a molar ratio n_E /n_O of less than 2 causes the relative number of moles of the atoms of the impurity elements 3 to be small, making the impurity element 3 as material for transporting Al less effective, and a molar ratio n_E /n_O of more than 1 × 10⁴ makes the relative number of moles of the atoms of the impurity element 3 too much great, both molar ratio ranges blocks the growth of the Al _x Ga_1-xN single crystal. Form this perspective, the molar ratio n_E /n_O is preferably between 3 and 1 × 10⁴ inclusive, and more preferably, is between 10 and 1 × 10⁴ inclusive. Herein, the number of moles of the atoms of oxygen contained in the source material 1 is calculated from the production of carbon monoxide generated by reacting the predetermined amount of the source material 1 with an excessive amount of carbon.
Furthermore, the atoms of oxygen contained in the source material 1 sometimes reduce above effect, of the action of the impurity element 3, that the present invention intends, as well as directly block the growth of the Al _x Ga_1-xN single crystal 4. For this reason, oxygen mole content α _MO , in the source material 1, defined by α _MO= 100 × n_O /n_M employing the number of moles n_M of the Al _y Ga_1-yN source 2 included in the source material 1 and the number of moles n_O of the atoms of oxygen contained in the source material 1 is preferably 1 mole % or less, and more preferably, 0.1 mole % or less.
In both particular situations in which the number of moles n_E of atoms of the impurity element 3 with respect to the number of moles n_A of Al atoms in the Al _y Ga_1-yN source 2 is particularly small (for example, a molar ratio n_E /n_A is less than 0.01 ), and in which the number of moles n_E of atoms of the impurity element 3 with respect to the number of moles n_O of the atoms of oxygen contained in the Al _y Ga_1-yN source 2 is small (for example, a molar ratio n_E /n_O is less than3), stable crystal growth is prevented to cause lower crystal growth rate, resulting in crystallinity degradation.
Herein, the impurity element 3 can be used in form of various compounds, in addition to form of single elemental substance. Oxides are not preferable, however, because they block crystal growth-for example, they increases oxygen content in the whole source material 1, and makes the above action the present invention intends of the impurity element 3 less effective.
Additionally, the source material 1 in which the impurity element 3 is added to the Al _y Ga_1-yN source 2 can be heat-treated prior to growth of the Al _x Ga_1-xN single crystal 4. Form the perspective of reducing any one specific element picked out from IVb element, and impurity element, excluding the impurity element 3, selected from the group consisting of IIa elements, and of activating the impurity element 3 in the source material 1 and improving dispersibility, heat-treating the source material 1 prior to the crystal growth is preferable. In the implementation of the heat-treatment of the source material 1 prior to the crystal growth, in the source material 1 that has undergone heat-treatment prior to crystal growth, ratio of the number of moles n_E of the atoms of the impurity element 3 to the number of moles n_A of the Al atoms in the Al _y Ga_1-yN source 2 (that is, molar ratio n_E /n_A ), oxygen mole content α _MO in the source material 1, and ratio of the number of moles n_E of the atoms of the impurity element 3 to the number of moles n_O of the atoms of oxygen contained in the source material 1 (that is, molar ratio n_E /n_O ) preferably fall within above ranges.
Moreover, the crucible 12 is not particularly limited, but from the perspective of stably growing the Al _x Ga_1-xN single crystal 4, the crucible 12 is preferably formed from materials that do not react with the Al _y Ga_1-yN source 2 or impurity element 3, or that suffer little degradation during growth of the Al _x Ga_1-xN single crystal 4 without discharging the impurity element 3 into the atmosphere in which crystal is grown, and preferably, is formed particularly from metal carbide. Preferable examples of the metal carbide for forming the crucible 12 include TiC, XrC, NbC, TaC, MoC, and WC. In case that principally because the impurity element 3 is discharged into the atmosphere in which crystal is grown, it is unintentionally provided to growing crystal, there is a possibility that content of the impurity element 3 in the atmosphere varies during crystal growth (for example, the content gradually overages), and thus crystal growth is blocked.

Disclosure Mode 2

Referring to Fig. 2, the source material 1 in which the Al _y Ga_1-yN source 2 and impurity element 3 are mixed together is arranged in crucible 12 in above step.
Because the material source 1 arranged in the crucible 12 is a mixture of the Al _y Ga_1-yN source 2 and impurity element 3, the distribution of the Al _y Ga_1-yN gas source and impurity element gas within the crucible 12 after the sublimation of the source material 1 is more readily uniformed, and thus the Al _x Ga_1-xN single crystal 4 is more stably grown.

Disclosure Mode 3

Referring to Fig. 3, the first source material compartment 12p, second source material compartment 12q and crystal-growth compartment 12r are provided in the crucible 12, with the ventilation openings 12a, 12b, and 12c being provided between the first and the second source material compartments 12p, 12q, and between at least one of them and the crystal-growth compartment 12r, and the Al _y Ga_1-yN source 2 is arranged in the first source material compartment 12p, with the impurity element 3 being arranged in the second source material compartment 12q.
Because the Al _y Ga_1-yN source 2 and impurity element 3 are arranged respectively in the first and second source material compartments 12p, 12q where gases in the compartments can be exchanged via the ventilation opening 12a, the distribution of the Al _y Ga_1-yN gas source and impurity element gas within the crucible 12 in which the source material 1 has sublimated can made more uniform without direct contact between the Al _y Ga_1-yN source 2 and impurity element 3, enabling more stable growth of the Al _x Ga_1-xN single crystal 4.
Herein, Fig. 3 illustrates the example in which the ventilation openings 12a, 12b, and 12c are provided respectively between the first and the second source material compartments 12p, 12q, between the first source material compartment 12p and the crystal-growth compartment 12r, and between the second source material compartment 12q and the crystal-growth compartment 12r, but in this embodiment mode, as to ventilation openings 12b and 12c, advantageously at least one of them may be provided.

Disclosure Mode 4

Referring to Fig. 4, an undersubstrate 9 is also placed in the crucible 12 and the Al _x Ga_1-xN single crystal 4 is grown on the undersubstrate 9. Herein, although Fig. 4 shows that the source material 1 in which the Al _y Ga_1-yN source 2 and impurity element 3 has been mixed is arranged in the crucible 12 (the source material 1 is arranged in the same manner as in Disclosure Mode 2), as to how to arrange the source material, the same manners as in Disclosure Mode 1 and 3 can be adopted.
Growing the Al _x Ga_1-xN single crystal 4 onto the undersubstrate 9 enables more stable growth of the Al _x Ga_1-xN single crystal 4. Herein, the undersubstrate 9 is not particularly limited as long as the Al _x Ga_1-xN single crystal 4 can be grown on it, so it may be any of a native substrate same with, and a non-native substrate different from, Al _x Ga_1-xN single crystal in chemical composition. From the perspective of improving crystallinity, a non-native substrate slightly differing from a native substrate or Al _x Ga_1-xN single crystal in lattice constant is preferable. Furthermore, from the perspective of producing bulk Al _x Ga_1-xN single crystal, the undersubstrate 9 is preferably a bulk substrate large in diameter. Form this perspective, SiC, Al₂O₃, GaN substrates are preferably utilized.
Employing an undersubstrate with a diameter of 2 inches or more enables growth of a bulk Al _x Ga_1-xN single crystal having a diameter of 2 inches or more. It should be understood that in manufacturing crystals, substrates, and other wafers, wafers with a diameter of 1 inch, 2inches, 4 inches, and other predetermined sizes are generally manufactured. That is to say, although 1 inch is 2.54 cm in unit conversion, a diameter of 2 inches means one of the sizes representing a diameter of wafers such as substrates and crystals, so that diameter, which is not limited exactly to 5.08 cm, includes manufacturing errors.
The III-nitride single crystal growth method involving the present invention is further furnished with a step of, referring to Figs. 1, 5, and 6, sublimating Al _t Ga_1-tN (0 < t ≤1) source 7 to grow onto the Al _x Ga_1-xN single crystal 4 grown by any of the growth methods in disclosure modes 1 through 4 a Al _s Ga_1-sN (0 < S ≤ 1) single crystal (5) with a lower concentration of the impurity element 3 compared with Al _x Ga_1-xN single crystal 4.
In the present invention, an Al_x2GGa_1-x2N single crystal 5 having favorable crystallinity, low concentration of the contained impurity element 3, and high general versatility can be grown onto the Al _x Ga_1-xN single crystal 4 of favorable crystallinity. Herein, the type and concentration of impurity element contained in the Al _x Ga_1-xN single crystal 4 and Al _s Ga_1-sN single crystal 5 can be measured by secondary ion mass spectroscopy (SIMS).
The step of sublimating the Al _t Ga_1-tN ((0 < t ≤ 1) source 7 to grow onto the Al _x Ga_1-xN single crystal 4 the Al _s Ga_1-sN (0 < S ≤ 1) single crystal 5 having a lower concentration of the contained impurity element 3 compared with the Al _x Ga_1-xN single crystal 4 is not particularly limited, so the step can be performed with, referring to Figs. 5 and 6, the Al _t Ga_1-tN source 7, not above impurity element, being arranged as source material in the crucible 12. Herein, referring to Fig. 5, Al _s Ga_1-sN single crystal is further grown onto the Al _x Ga_1-xN single crystal 4 that has been grown onto the undersubstrate 9. Moreover, referring to Fig. 6, the grown Al _x Ga_1-xN single crystal 4 is processed into a substrate, and then the Al _s Ga_1-sN single crystal 5 is further grown onto this substrate.
Additionally, the Al _s Ga_1-sN single crystal grown on the Al _x Ga_1-xN single crystal may be same (s = x) with, and be different (s ≠ x) from, the Al _x Ga_1-xN single crystal 4 in chemical composition. From the perspective of growing Al _s Ga_1-sN single crystal of favorable crystallinity, however, the chemical composition of the Al _s Ga_1-sN single crystal is preferably close to, and more preferably, similar to that of the Al _x Ga_1-xN single crystal. The chemical composition of the Al _t Ga_1-tN source 7 and that of the Al _s Ga_1-sN single crystal 5 produced from it are same with each other when s = t = 1, but differ from each other except when s = t = 1 generally in accordance with the conditions on which the Al _t Ga_1-tN source 7 is sublimated, and with the conditions on which the Al _s Ga_1-sN single crystal 5 is grown. Once the sublimation conditions on the Al _t Ga_1-tN source 7 and growth conditions on the Al _s Ga_1-sN single crystal 5 are determined, the chemical composition of the Al _t Ga_1-tN source 7 for producing the Al _s Ga_1-sN single crystal 5 of the predetermined chemical composition is defined.

Example 1

Referring to Figs. 1 and 4, AlN powder (the Al _y Ga_1-yN source 2) and Si powder (the impurity element 3) were mixed so that molar ratio n_E /n_A of Si atoms (atoms of the impurity element 3) in the Si powder to Al atoms in the AlN powder (the Al _y Ga_1-yN source 2) was made 0.05, and were arranged as the source material 1 in the bottom part of the WC crucible 12. Furthermore, a SiC substrate 2 inches (5.08 cm) in diameter was arranged as the undersubstrate 9 in the top part of the crucible 12. Herein, oxygen mole percent α _MO in the AlN powder and Si powder (the source material 1) was 0.1, and molar ratio n_E /n_O of Si atoms (atoms of the impurity element 3) of the Si powder to the atoms of oxygen contained in the AlN powder and Si powder (source material 1) was 20. In addition, WC material that is an undersubstrate protector 16 is closely attached to the back side of the SiC substrate (the undersubstrate 9).
Next, with N₂ gas being continuously passed into the reaction chamber 11, the temperature in the crucible 12 was raised employing the high-frequency coils 14. While the temperature in the crucible 12 was rising, with temperature in the part of the crucible 12 where the SiC substrate (the undersubstrate 9) was arranged being kept higher than that in the part of the crucible 12 where the source material 1 was arranged, the front side of the SiC substrate (the under substrate 9) was cleaned by means of etching, and at the same time the impurities discharged from the SiC substrate (the undersubstrate 9) and the inside of the crucible 12 were removed though the ventilation opening 12e.
Subsequently, the temperature in the part of the crucible 12 where the source material 1 was arranged was brought to 2100°C, and the temperature in the part of the crucible 12 where the SiC substrate (the undersubstrate 9) was arranged was brought to 2000°C, to sublimate AlN and Si from the source material 1, and the AlN was solidified again on the SiC substrate (the undersubstrate 9 ) arranged in the top part of the crucible 12 to grow AlN single crystal (the Al _x Ga_1-xN single crystal 4). The N₂ gas was passed into the reaction chamber outside the crucible 12 continuously also during AlN sigle crystal (the Al _x Ga_1-xN single crystal 4) growth, and the amounts of N₂ gas introduction and emission is controlled so that the partial pressure of gas in the reaction chamber 11 outside the crucible 12 is brought to a level of 101.3 hPa to 1013 hPa. After 30 h AlN crystal (the Al _x Ga_1-xN single crystal 4) growth under above crystal growth conditions, the crucible 12 was cooled to room temperature, and thus the AlN crystal was obtained.
The obtained AlN single crystal (the Al _x Ga_1-xN single crystal 4) was a large 2 inches (5.08 cm) in diameter × 4 mm in thickness with a uniform thickness, and its growth rate was 133 µm/hr. The full-width at half-maximum of X-ray diffraction peak on the AlN single crystal (0002) face is a small 70 arcsec, and crystallinity was preferable. Furthermore, the AlN single crystal dislocation density, which was calculated by etch-pit density (EPD: the method of calculating as dislocation density the density of pits forming on front side as a result of etching), was a low 5.0 × 10⁵ cm^-2. The results are set forth in Table 1.

Comparative example 1

Apart from utilizing as the source material 1 only AlN powder (the Al _y Ga_1-yN source 2) in which the impurity element 3 was not included, AlN single crystal (the Al _x Ga_1-xN single crystal 4) was grown in the same manner as in Embodiment 1. Although the obtained AlN single crystal (the Al _x Ga_1-xN single crystal 4) was 2 inches (5.08 cm) in diameter, its thickness is nonuniform-0.4 mm on average-and its growth rate was 13 µm/hr. In addition, the areas in which AlN single crystal has not grown was found on the SiC substrate (the undersubstrate 9). The full-width at half-maximum of X-ray diffraction peak on the AlN single crystal (0002) face is a great 500 arcsec, and crystallinity was spoiled. Furthermore, polycrystal was scattered in some areas on the AlN single crystal (0002) face. Moreover, the AlN single crystal dislocation density was a high at 1.0 × 10⁹ cm^-2. The results are set forth in Table 1.

Example 2

Apart from employing as the source material 1 the mixture in which the AlN powder (the Al _y Ga_1-yN source 2) and Si powder (impurity element 3) were mixed so that molar ratio n_E /n_A of Si atoms in the Si powder to Al atoms in the AIN powder was 0.01 (oxygen mole percent α _MO in the source material 1 was 0.1 mol %, and molar ratio n_E /n_O of Si atoms in the Si powder to the atoms of oxygen contained in the source material 1 was 4), AlN single crystal (the Al _x Ga_1-xN single crystal 4) was grown in the same manner as in Embodiment 1. The obtained AlN single crystal (the Al _x Ga_1-xN single crystal 4) was a large 2 inches (5.08 cm) in diameter × 3 mm in thickness with a uniform thickness, and its growth rate was 100 µm/hr. The full-width at half-maximum of X-ray diffraction peak on the AlN single crystal (0002) face was a small 500 arcsec, and crystallinity was preferable. Furthermore, the AlN single crystal dislocation density was a low 6.0 × 10⁵ cm^-2. The results are set forth in Table 1.

Example 3

Apart from employing as the source material 1 the mixture in which AlN powder (the Al _y Ga_1-yN source 2) and Si powder (the impurity element 3) were mixed so that molar ratio n_E /n_A of Si atoms in the Si powder to Al atoms in the AIN powder was 0.3 (oxygen mole percent α _MO in the source material 1 was 0.1 mol %, and molar ratio n_E /n_O of Si atoms in the Si powder to the atoms of oxygen contained in the source material 1 was 120), AlN single crystal (the Al _x Ga_1-xN single crystal 4) was grown in the same manner as in Embodiment 1. The obtained AlN single crystal (the Al _x Ga_1-xN single crystal 4) was a large 2 inches (5.08 cm) in diameter × 4.5 mm in thickness with a uniform thickness, and its growth rate was 150 µm/hr. The full-width at half-maximum of X-ray diffraction peak on the AlN single crystal (0002) face was a small 100 arcsec, and crystallinity was preferable. Furthermore, the AlN ingle crystal dislocation density was a low 7.0 × 10⁵ cm^-2. The results are set forth in Table 1.

Example 4

Apart from employing as the source material 1 the mixture in which AlN powder (the Al _y Ga_1-yN source 2) and Si powder (the impurity element 3) were mixed so that molar ratio n_E /n_A of Si atoms in the Si powder to A1 atoms in the AlN powder was 0.5 (oxygen mole percent α _MO in the source material 1 was 0.1 mol %, and molar ratio n_E /n_O of Si atoms in the Si powder to the atoms of oxygen contained in the source material 1 was 200), AlN single crystal (the Al _x Ga_1-xN single crystal 4) was grown in the same manner as in Embodiment 1. The obtained AlN single crystal (the Al _x Ga_1-xN single crystal 4) was a large 2 inches (5.08 cm) in diameter × 5 mm in thickness with a uniform thickness, and its growth rate was 166 µm/hr. The full-width at half-maximum of X-ray diffraction peak on the AlN single crystal (0002) face was a small 120 arcsec, and crystallinity was preferable. Furthermore, the AlN single crystal dislocation density was a low 8.0 × 10⁵ cm^-2. The results are set forth in Table 1.

Example 5

Apart from employing as the source material 1 the mixture in which AlN powder (the Al _y Ga_1-yN source 2) and C (carbon) powder (the impurity element 3) were mixed so that molar ratio n_E /n_A of C atoms in the C powder to Al atoms in the AlN powder was 0.01 (oxygen mole percent α _MO in the source material 1 was 0.1 mol %, and molar ratio n_E /n_O of C atoms in the C powder to atoms in the oxygen contained in the source material 1 was 4), AlN single crystal (the Al _x Ga_1-xN single crystal 4) was grown in the same manner as in Embodiment 1. The obtained AlN single crystal (the Al _x Ga_1-xN single crystal 4) was a large 2 inches (5.08 cm) in diameter × 4.8 mm in thickness with a uniform thickness, and its growth rate was 150 µm/hr. The full-width at half-maximum of X-ray diffraction peak on the AlN single crystal (0002) face was a small 45 arcsec, and crystallinity was preferable. Furthermore, the AlN single crystal dislocation density was a low 9.0 × 10⁴ cm^-2. The results are set forth in Table 1.

Example 6

Apart from employing as the source material 1 the mixture in which AlN powder (the Al _y Ga_1-yN source 2) and C (carbon) powder (the impurity element 3) were mixed so that molar ratio n_E /n_A of C atoms in the C powder to Al atoms in the AlN powder was 0.05 (oxygen mole percent α _MO in the source material 1 was 0.1 mol %, and the molar ratio n_E /n_O of C atoms in the C powder to atoms of the oxygen contained in the source material 1 was 20), AlN single crystal (the Al _x Ga_1-xN single crystal 4) was grown in the same manner as in Embodiment 1. The obtained AlN single crystal (the Al _x Ga_1-xN single crystal 4) was a large 2 inches (5.08 cm) in diameter × 9 mm in thickness with a uniform thickness, and its growth rate was 300 µm/hr. The full-width at half-maximum of X-ray diffraction peak on the AlN single crystal (0002) face was a small 30 arcsec, and crystallinity was preferable. Furthermore, the AlN single crystal dislocation density was a low 5.0 × 10⁴ cm^-2. The results are set forth in Table 1.

Example 7

Apart from employing as the source material 1 the mixture in which AlN powder (the Al _y Ga_1-yN source 2) and C (carbon) powder (the impurity element 3) were mixed so that molar ratio n_E /n_A of C atoms in the C powder to Al atoms in the AlN powder was 0.3 (oxygen mole percent α _MO in the source material 1 was 0.1 mol %, and molar ratio n_E /n_O of C atoms in the C powder to atoms of the oxygen contained in the source material 1 was 120), AlN single crystal (the Al _x Ga_1-xN single crystal 4) was grown in the same manner as in Embodiment 1. The obtained AlN single crystal (the Al _x Ga_1-xN single crystal 4) was a large 2 inches (5.08 cm) in diameter × 10.5 mm in thickness with a uniform thickness, and its growth rate was 350 µm/hr. The full-width at half-maximum of X-ray diffraction peak on the AlN single crystal (0002) face was a small 30 arcsec, and crystallinity was preferable. Furthermore, the AlN single crystal dislocation density was a low 6.0 × 10⁴ cm^-2. The results are set forth in Table I.

Example 8

Apart from employing as the source material 1 the mixture in which AlN powder (the Al _y Ga_1-yN source 2) and C (carbon) powder (the impurity element 3) were mixed so that the molar ratio n_E /n_A of C atoms in the C powder to Al toms in the AlN powder was 0.5 (oxygen mole percent α _MO in the source material 1 was 0.1 mol %, and molar ratio n_E /n_O of C atoms in the C powder to atoms of the oxygen contained in the source material 1 was 200), AlN single crystal (the Al _x Ga_1-xN single crystal 4) was grown in the same manner as in Embodiment 1. The obtained AlN single crystal (the Al _x Ga_1-xN single crystal 4) was a large inches (5.08 cm) in diameter × 12 mm in thickness with a uniform thickness, and its growth rate was 400 µm/hr. The full-width at half-maximum of X-ray diffraction peak on the AlN single crystal (0002) face was a small 45 arcsec, and crystallinity was preferable. Furthermore, the AlN single crystal dislocation density was a low 1.0 × 10⁵ cm^-2. The results are set forth in Table I.

Example 9

Apart from employing as the source material 1 the mixture in which AlN powder (the Al _y Ga_1-yN source 2) and Ge powder (the impurity element 3) were mixed so that molar ratio n_E /n_A of Ge atoms in the Ge powder to Al atoms in the AlN powder was 0.05 (oxygen mole percent α _MO in the source material 1 was 0.1 mol %, and molar ratio n_E /n_O of Ge atoms in the Ge powder to atoms of the oxygen contained in the source material 1 was 20), AlN single crystal (the Al _x Ga_1-xN single crystal 4) was grown in the same manner as in Embodiment 1. The obtained AlN single crystal (the Al _x Ga_1-xN single crystal 4) was a large 2 inches (5.08 cm) in diameter × 6 mm in thickness with a uniform thickness, and its growth rate was 200 µm/hr. The full-width at half-maximum of X-ray diffraction peak on the AlN single crystal (0002) face was a small 50 arcsec, and crystallinity was preferable. Furthermore, the AlN single crystal dislocation density was a low 8.0 × 10⁴ cm^-2. The results are set forth in Table II.

Example 10

Apart from employing as the source material 1 the mixture in which AlN powder (the Al _y Ga_1-yN source 2) and Ca powder (the impurity element 3) were mixed so that molar ratio n_E /n_A of Ca atoms in the Ca powder to Al atoms in the AlN powder was 0.05 (oxygen mole percent α _MO in the source material 1 was 0.1 mol %, and molar ratio n_E /n_O of Ca atoms in the Ca powder to atoms of the oxygen contained in the source material 1 was 20), AlN single crystal (the Al _x Ga_1-xN single crystal 4) was grown in the same manner as in Embodiment 1. The obtained AlN single crystal (the Al _x Ga_1-xN single crystal 4) was a large 2 inches (5.08 cm) in diameter × 3 mm in thickness with a uniform thickness, and its growth rate was 100 µm/hr. The full-width at half-maximum of X-ray diffraction peak on the AlN single crystal (0002) face was a small 120 arcsec, and crystallinity was preferable. Furthermore, the AlN single crystal dislocation density was a low 6.0 × 10⁵ cm^-2. The results are set forth in Table II.

Example 11

Apart from employing as the source material 1 the mixture in which AlN powder (the Al _y Ga_1-yN source 2) and Mg powder (the impurity element 3) were mixed so that molar ratio n_E /n_A of Mg atoms in the Mg powder to Al atoms in the AlN powder was 0.05 (oxygen mole percent α _MO in the source material 1 was 0.1 mol %, and molar ratio n_E /n_O of Mg atoms in the Mg powder to atoms of the oxygen contained in the source material 1 was 20), AlN single crystal (the Al _x Ga_1-xN single crystal 4) was grown in the same manner as in Embodiment 1. The obtained AlN single crystal (the Al _x Ga_1-xN single crystal 4) was a large 2 inches (5.08 cm) in diameter × 2 mm in thickness with a uniform thickness, and its growth rate was 67 µm/hr. The full-width at half-maximum of X-ray diffraction peak on the AlN single crystal (0002) face was a small 150 arcsec, and crystallinity was preferable. Furthermore, the AlN single crystal dislocation density was a low 7.0 × 10⁵ cm^-2. The results are set forth in Table II.

Example 12

Apart from employing as the source material 1 the mixture in which AlN powder (the Al _y Ga_1-yN source 2) and Si and Ca powders (impurity element 3) were mixed as the source material 1 so that molar ratio n_E /n_A of Si atoms in the Si powder to, and that of Ca atoms in the Ca powder to, Al atoms in the AlN powder were respectively 0.025 and 0.025 (oxygen mole percent α _MO in the source material 1 was 0.1m mol %, and molar ratio n_E /n_O of Si atoms of the Si powder to, and that of Ca atoms of the Ca powder to, atoms of the oxygen contained in the source material 1 were respectively 10 and 10), AlN single crystal (the Al _x Ga_1-xN single crystal 4) was grown in the same manner as in Embodiment 1. The obtained AlN single crystal (the Al _x Ga_1-xN single crystal 4) was a large 2 inches (5.08 cm) in diameter × 4.5 mm in thickness with a uniform thickness, and its growth rate was 150 µm/hr. The full-width at half-maximum of X-ray diffraction peak on the AlN single crystal (0002) face was a small 70 arcsec, and crystallinity was preferable. Furthermore, the AlN single crystal dislocation density was a low 5.0 × 10⁵ cm^-2. The results are set forth in Table II.

Example 13

Apart from employing as the source material 1 the mixture in which AlN powder (the Al _y Ga_1-yN source 2) and C and Ca powders (impurity element 3) were mixed so that molar ratio n_E /n_A of C atoms in the C powder to, and that of Ca atoms in the Ca powder to, Al atoms in the AlN powder was respectively 0.025 and 0.025 (oxygen mole percent α _MO in the source material 1 was 0.1 mol %, and molar ratio n_E /n_O of C atoms in the C powder to, and that of Ca atoms in the Ca powder to, atoms of the oxygen contained in the source material 1 was respectively 10 and 10), AlN single crystal (the Al _x Ga_1-xN single crystal 4) was grown in the same manner as in Embodiment 1. The obtained AlN single crystal (the Al _x Ga_1-xN single crystal 4) was a large 2 inches (5.08 cm) in diameter × 6 mm in thickness with a uniform thickness of 6 mm, and its growth rate was 200 µm/hr. The full-width at half-maximum of X-ray diffraction peak on the AlN single crystal (0002) face was a small 45 arcsec, and crystallinity was preferable. Furthermore, the AlN single crystal dislocation density was s low 8.0 × 10⁴ cm^-2. The results are set forth in Table II.

Example 14

Apart from employing as the source material 1 the mixture in which Al_0.65Ga_0.35N powder (the Al _y Ga_1-yN source 2) and C powder were mixed so that molar ratio n_E /n_A of C atoms in the C powder to Al atoms in the AlN powder was 0.05 (oxygen mole percent α _MO in the source material 1 was 0.1 mol %, and molar ratio n_E /n_O of C atoms in the C powder to atoms of oxygen contained in the source material 1 was 20), AlN single crystal (the Al _x Ga_1-xN single crystal 4) was grown in the same manner as in Embodiment 1. The chemical composition of the obtained single crystal measured Al_0.8Ga_0.2N by x-ray photoelectron Spectroscopy. That is to say, the obtained Al _x Ga_1-xN single crystal 4 included Al atoms at a greater ratio compared with that of the Al _y Ga_1-yN source 2. The possible reason is that C atoms promoted the transportation of Al. The obtained Al_0.8Ga_0.2N single crystal (the Al _x Ga_1-xN single crystal 4) was a large 2 inches (5.08 cm) in diameter × 8 mm in thickness with a uniform thickness, and its growth rate was 266 µm/hr. The full-width at half-maximum of X-ray diffraction peak on the AlN single crystal (0002) face was a small 50 arcsec, and crystallinity was preferable. Furthermore, the Al_0.8Ga_0.2N single crystal dislocation density was a low 1.0 × 10⁵ cm^-2. The results are set forth in Table II.
As is clear from Tables I and II, in Al _x Ga_1-xN single crystal sublimation growth, the presence, as source material to be sublimated, of Al _y Ga_1-yN source, of any specific element picked out from IVb elements, and of at least a single kind of impurity element selected from the group consisting of IIa elements heightened crystal growth rate increases, and made it possible to obtain low-dislocation-density Al_xGa_1-xN single crystal of favorable crystallinity. Furthermore, making molar ratio n_E /n_A of the impurity element atoms to Al atoms in the Al _y Ga_1-yN source included in the source material to be sublimated 0.01 to 0.5 inclusive, and/or making molar ratio n _E /n _O of the impurity element atoms to the atoms oxygen contained in the source material to be sublimated 1 × 10⁴ or less, kept crystal growth rate high, and enabled obtaining lower-dislocation-density Al _x Ga_1-xN single crystal of favorable crystallinity.

Example 15

As in Example 5, an AlN single crystal (the Al _x Ga_1-xN single crystal 4) 2inches (5.08 cm) in diameter × 4.8 mm in thickness was grown. In this AlN single crystal (the Al _x Ga_1-xN single crystal 4), its dislocation density was a low 9.0 × 10⁴ cm^-2, and as to impurity concentration measured by SIMS, carbon atom concentration was approximately 1 × 10¹⁸ cm^-3, and oxygen atom concentration was 1 × 10¹⁷ cm^-3 or less. Referring to Fig. 5, subsequently, AlN powder was sublimated to grow another AlN single crystal (the Al _s Ga_1-sN single crystal 5) onto the AlN single crystal (the Al _x Ga_1-xN single crystal 4). Apart from making the temperature in the part of the crucible 12 where Al _t Ga_1-tN source 7 was arranged 2200°C, and from making the temperature in the part end of the crucible 12 where the Al _x Ga_1-xN single crystal 4 was grown 2050°C, crystal growth conditions was established as in Example 5. The obtained AlN single crystal (the Al _s Ga_1-sN single crystal 5), which was a large 2 inches (5.08 cm ) in diameter × 1 mm in thickness with a uniform thickness. The AlN single crystal (the Al _s Ga_1-sN single crystal 5) dislocation density was a low 2.0 × 10⁵ cm^-2, and as to impurity concentration measured by SIMS, both carbon atom and oxygen atom concentrations were an extremely low 1 × 10¹⁷ cm^-3. As just described, as a result of sublimating the source material 1 including the Al _y Ga_1-yN source 2 and at least a single kind of impurity element 3 selected form the group consisting of IVb elements and IIa elements to grow the Al _x Ga_1-xN single crystal 4, and of sublimating the Al _t Ga_1-tN source 7 to grow onto the Al _x Ga_1-xN single crystal 4 the Al _s Ga_1-sN single crystal 5 in which the impurity element 3 was contained at lower concentrations 3 compared with those in the Al _x Ga_1-xN single crystal 4, the Al _s Ga_1-sN single crystal 5 low in both dislocation density and impurity concentration can be obtained.
The presently disclosed embodiments and implementation examples should in all respects be considered to be illustrative and not limiting. The scope of the present invention is set forth not by the foregoing description but by the scope of the patent claims, and is intended to include meanings equivalent to the scope of the patent claims and all modifications within the scope.

Claims

A III-nitride single-crystal growth method, comprising:
a step of placing source material (1) in a crucible (12);

a step of sublimating the source material (1) to grow an Al _x Ga_1-xN (0 < x s 1) single crystal (4) in the crucible (12), wherein

the source material (1) includes an Al_yGa_1-yN (0 < y s 1) source (2), and an impurity element (3), and

the impurity element (3) is a single kind element selected from the group consisting of Si, C, and Ge; and

a step of sublimating an Al_tGa_1-tN (0 < t s 1) source (7) to grow onto the Al_xGa_1-xN single crystal (4) a Al_sGa_1-sN (0 < s ≤ 1) single crystal (5) in which the impurity element (3) is contained at lower concentration compared with that in the Al_xGa_1-xN single crystal (4);

wherein in the source material (1), a ratio n _E/n _A of the number of moles n_E of atoms of the impurity element (3) to the number of moles n _A of the Al atoms in the Al_yGa_1-yN source (2) is between 0.01 to 0.5 inclusive, and

wherein a ratio n _E/n _O of the number of moles n _E of atoms of the impurity element (3) to the number of moles n _o of atoms of the oxygen contained in the material source (1) is between 2 and 1 × 10⁴ inclusive.
A III-nitride single-crystal growth method as set forth in claim 1, wherein:
a first source material compartment (12p), a second source material compartment (12q), and a crystal-growth compartment (12r) are provided in the crucible 12;

ventilation openings (12a, 12b, 12c) are provided between the first source material compartment (12p) and the second source material compartment (12q), and between at least one source material compartment of the first and the second source material compartments (12p, 12q) and the crystal-growth compartment (12r); and

the Al_yGa_1-yN (0 < y ≤ 1) source (2) is arranged in the first source material compartment (12p), and the impurity element (3) is arranged in the second source material compartment (12q).
A III-nitride single-crystal growth method as set forth in claim 1, wherein the source material (1) is a mixture of the Al_yGa_1-yN source (2) and the impurity element (3).
A III-nitride single-crystal growth method as set forth in claim 1, further comprising a step of disposing an undersubstrate (9) in the crucible (12) to grow the Al _x Ga_1-xN single crystal (4) onto the under substrate (9).